how to connect a microphone to a circuit?

Discussion in 'The Projects Forum' started by baggio2, Feb 15, 2009.

  1. baggio2

    Thread Starter Active Member

    Dec 25, 2008
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    hi..i made a infrared audio transmitter but i dont know how to connect an electret microphone...this is the circuit and microphone...i guess i need to use a resistor and capacitor do connect it...could tell me what resistor and capacitor values are gonna be?
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    The opamp circuit is inverting with a low input impedance. It should be non-inverting with a high input impedance. Then the mic can be capacitor-coupled to its input and have a filtered supply fed through a 10k resistor to the mic.

    A lousy old 741 opmap is too noisy (hissss) for use as a mic preamp. You should use a low noise audio opamp like a TL071.

    The wire on the mic that is connected to its metal case is its ground wire.
     
  3. baggio2

    Thread Starter Active Member

    Dec 25, 2008
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    0
    thanks..ur circuit is a preamp right? i need to generate a square wave by a schmitt trigger for 555 input...i mean i should connect ur circuit output to a schmitt input..or to 555 input?
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    A 555 is not an analog device. To be able to transmit audio with an IR led you have to convert the audio signal into a digital one and then transmit it with the IR led.

    Note that you can to it by connecting the IR led to the output of the transmitter as its light intensity to be varied with the audio signal but this won't be good.

    The circuit you have won't work.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The 555 oscillator has its frequency modulated (FM) by the preamp audio signal. Then the IR LED is FM modulated.

    Then you need an IR receiver and an FM receiver circuit that is tuned to the average 555 frequency.
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    Ohhh yes Audioguru is right :p

    I haven't realized that you drive the control pin of the 555, I though you drive the trigger. :eek:


    Disconnect the bottom side of the microphone from ground and connect it between the 5.6K resistors. Also, put a 10uF capacitor between the microphone and P1.
     
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